Trust & transparency

Sources & References

Every figure on GreenCalcs traces to a primary, authoritative source. This page lists the government, national-laboratory and industry references behind our calculators and guides, organized by topic, so you can verify any claim yourself.

SCMaintained by Sarah Chen, Energy Analyst Primary sources: IRS, DOE, NREL, EIA, DSIRE, EPA
Updated October 2026 — federal credits have ended. The One Big Beautiful Bill Act (signed July 4, 2025) ended the 30% federal Residential Clean Energy Credit (25D: solar, batteries, geothermal) and the Energy Efficient Home Improvement Credit (25C: air-source heat pumps, up to $2,000) for anything installed after December 31, 2025. Systems completed by Dec 31, 2025 can still be claimed on a 2025 return. Any 30% or $2,000 figure on this page applies only to those installs — our calculators now default to $0 federal credit. What is still available in 2026 →
Why this mattersWe don't cite installer marketing — we cite the source. Tax rules come from the IRS, incentives from DSIRE, electricity rates from the EIA, costs and reliability from NREL, and heat pump data from the DOE and ENERGY STAR. See how we use them in our methodology.
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Federal tax credits, the OBBBA & the IRA

  1. IRS — FAQs on the modification of Sections 25C, 25D and others under the One Big Beautiful Bill (Public Law 119-21, July 4, 2025)
  2. IRS — Residential Clean Energy Credit (25D, ended for installs after Dec 31, 2025)
  3. IRS — Energy Efficient Home Improvement Credit (25C, ended for property placed in service after Dec 31, 2025)
  4. IRS — Form 5695 & Instructions
  5. IRS — Alternative Fuel Vehicle Refueling Property Credit
  6. U.S. Dept. of Energy — Home Energy Rebates (HEAR / HEEHRA)

State & local incentives

  1. DSIRE — Database of State Incentives for Renewables & Efficiency
  2. EPA — Solar for All
  3. ENERGY STAR — Rebate Finder
  4. U.S. Dept. of Energy — Low-Income Community Energy Solutions

Solar performance, technology & reliability

  1. NREL — Photovoltaic Research
  2. NREL — PV Module Reliability
  3. U.S. Dept. of Energy — Homeowner's Guide to Going Solar
  4. U.S. Dept. of Energy — SolarAPP+ Instant Permitting
  5. U.S. Dept. of Energy — Solar Energy & the Circular Economy
  6. EPA — Solar Panel Recycling

Heat pumps & home heating

  1. U.S. Dept. of Energy — Heat Pump Systems
  2. U.S. Dept. of Energy — Air-Source Heat Pumps
  3. ENERGY STAR — Heat Pumps
  4. NEEP — Cold Climate Air-Source Heat Pump List
  5. CEE — Residential Heating & Cooling Specifications
  6. EPA — Section 608 Refrigerant Handling

Electricity prices & energy data

  1. EIA — Electricity Data
  2. EIA — Electric Power Monthly
  3. NREL — Solar Resource Data & Tools

Consumer protection & safety

  1. Federal Trade Commission — Solar Power for Your Home
  2. NFPA / National Electrical Code
  3. FEMA — Building Resilience
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How we use these

Our Methodology →

How we turn these sources into calculators and guides.

Guides →

40 in-depth guides, each citing its own sources.

Glossary →

Plain-English definitions of the technical terms.

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